This invention relates to substantially pure, isolated populations of antigen presenting cells (“APC” cells), methods for obtaining such purified cell populations, and methods for treating diseases of the gastrointestinal tract using inhibitors of the CD70 antigen expressed on activated B cells and T lymphocytes, and in particular, a method for treating and preventing inflammatory bowel disease using CD70 inhibitors.
The intestinal immune response is different from the immune response of other organs in the body, but the basis for the distinctiveness of the intestinal immune response is not fully understood.
Lymphocytes in the intestinal mucosa possess several features that are distinct from their counterparts in the secondary lymphoid organs. It has been suggested that the activation pathways of mucosal T cells are different from those of peripheral T cells. In contrast to peripheral T cells, intestinal mucosal T cells are resistant to TCR-CD3 stimulation, but proliferate vigorously and secrete pro-inflammatory cytokines after CD2 stimulation. Similarly, intestinal mucosal T cells express distinctive adhesion molecules, and their costimulatory requirements are different than peripheral T cells. Again, for instance, the systemic administration of soluble protein antigen without adjuvant induces differentiated cytotoxic T cells in intestinal mucosa, but not in spleen and lymph nodes. Finally, transactivation of IFN-γ expression in peripheral T cells and mucosal T cells occurs through the use of different cis-regulatory elements, and requires the recruitment of different transactivating factors. One possible reason for these differences is that T cells may be stimulated with different types of antigen presenting cells in the mucosa and peripheral regions of the body.
Different subsets of dendritic cells have been identified in intestinal lymphoid organs. In addition to the myeloid dendritic cells and the lymphoid dendritic cells found in the spleen and lymph nodes, Peyer's patch and mesenteric lymph nodes also contain a novel population of dendritic cells. However, Peyer's patch dendritic cells differ from splenic and lymph node dendritic cells in their ability to induce cytokine production. For instance, in contrast to splenic dendritic cell-stimulated T cells, which produce IFN-γ, Peyer's patch dendritic cell-primed T cells secrete predominantly IL-10 and L-4. Further, after ligation of the costimulatory molecule, RANK, Peyer's patch dendritic cells produce IL-10, while splenic dendritic cells produce IL-12. Thus, while splenic dendritic cells provide a stimulatory environment, Peyer's patch dendritic cells generally provide an inhibitory environment. Given this fact, it is surprising that the intestinal mucosal T cell response to infections is more robust and more prolonged than in peripheral cells, despite an equivalent antigen load.
Dendritic cells are antigen-presenting cells found in all tissues and organs of the body. The dendritic cells present antigens for T lymphocytes, i.e., they process and present antigens, and stimulate responses from naive and memory T cells. In addition to their role in antigen presentation, dendritic cells directly communicate with non-lymph tissue and survey non-lymph tissue for an injury signal (e.g., ischemia, infection, or inflammation), or tumor growth. Once signaled, dendritic cells initiate an immune response by releasing inflammatory cytokines which trigger lymphocytes and myeloid cells. Various immunodeficiencies are thought to result from the loss of dendritic cell function.
One of the important features of dendritic cell maturation is the upregulation of costimulatory molecules. Although, as noted above, differences in cytokine induction have been described, so far no differences in the induction of costimulatory molecules have been reported between peripheral and intestinal dendritic cells. CD70 is also known to be a TNF-related costimulatory ligand. CD70 has been shown to be expressed by activated murine dendritic cells in vitro, and the persistent expression of CD70 in transgenic mice results in the activation of naïve T cells, and the expansion of effector memory cells, leading ultimately to the exhaustion of the naïve T cell pool. However, the constitutive CD70 expression by immune cells in vivo has not been reported.
Dendritic cell populations in the intestinal mucosa remain poorly characterized. Although dendritic cells from lamina propria tissue have been shown to be capable of penetrating the intestinal epithelial layer to sample luminal bacteria, no distinct dendritic cell subsets have so far been described in the lamina propria compartment.
An understanding of the immune response in the gastrointestinal tract is essential in order to develop effective treatments for intestinal diseases such as inflammatory bowel disease. Inflammatory bowel disease is a medical condition that results when cells involved in inflammation and immune response infiltrate the lining of the gastrointestinal tract. This infiltration thickens the bowel lining and interferes with liquid absorption and motility, thereby disrupting the normal functioning of the bowel.
Accordingly, it is an objective of this invention to provide methods for treating diseases of the gastrointestinal tract using inhibitors of CD70, and in particular, to methods for treating inflammatory bowel disease using such inhibitors.
It is a further objective of this invention to provide substantially pure, isolated populations of unique antigen presenting cells found in the intestinal mucosa, and methods for obtaining such purified cell populations.